docs: def add_cell_footer(self):
          """
          Add footer cell
          """
  
          # check if there's already a cell footer... if true, do not add a second cell footer.
          # this situation happens when exporting to ipynb and then importing from ipynb.
  
          logging.info('Adding footer cell')
  
          for cell in self.nb['cells']:
              if cell.cell_type == 'markdown':
                  if 'pynb_footer_tag' in cell.source:
                      logging.debug('Footer cell already present')
                      return
  
          m = """
  
              ---
              * **Notebook class name**: {class_name}
              * **Notebook cells name**: {cells_name}
              * **Execution time**: {exec_begin}
              * **Execution duration**: {exec_time:.2f}s
              * **Command line**: {argv}
              [//]: # (pynb_footer_tag)
              """
          self.add_cell_markdown(
              m.format(exec_time=self.exec_time, exec_begin=self.exec_begin_dt, class_name=self.__class__.__name__,
                       argv=str(sys.argv), cells_name=self.cells_name))